The present invention relates to a toner recycling control system of an electrophotographic apparatus which collects residual developer remaining after development and after transfer, adjusts the concentration of the collected developer, and feeds the concentration-adjusted developer back to a regular process.
A liquid-development electrophotographic apparatus uses, as developer, toner liquid which is formed through dispersion of toner particles in carrier liquid. The developer undergoes concentration adjustment beforehand so as to be suitable for use in development, and is subsequently fed to a development section. Development involves transfer of a portion of toner particles and carrier liquid to an image-bearing body (a photosensitive drum), and residual developer is collected from the development section. The developer collected from the development section shows a change in concentration attributable to loss of transferred toner particles (and a portion of carrier), the amount of the loss depending on the ratio between an image area and a non-image area on a print surface. That is, the developer collected at this point of time is not suitable for use in development and thus cannot be reused as is.
The collected developer may be completely disposed of. However, desirably, in order to recycle developer in view of cost and environmental concerns, the developer collected within the apparatus undergoes concentration adjustment and is fed back to the development section.
In a conventional electrophotographic apparatus using a low-viscosity liquid developer, a low-concentration, low-viscosity liquid developer is excessively fed to a latent area on an image-bearing body to thereby form an image. At this time, excess liquid developer is collected and fed back to a developer-bearing body (a developing roller). Repetitive, circulative feed and collection of liquid developer involves consumption of solid matter contained in the liquid developer, resulting in a failure to provide required image density. Therefore, the concentration of the liquid developer is adjusted to a predetermined level through replenishment with concentrated liquid developer, and the thus-adjusted developer is fed to the developer-bearing body.
As mentioned above, according to conventional practice, a low-viscosity liquid developer is excessively fed to a latent area. Thus, the concentration of the fed liquid developer may vary within a certain tolerance. However, since a low-viscosity liquid developer is a volatile liquid, volatilized liquid must be collected within the apparatus, leading to an increase in the size of the apparatus.
By contrast, in a liquid developing apparatus that uses a nonvolatile, high-concentration, high-viscosity liquid developer, the liquid developer is applied, in the form of a thin layer, to a developer-bearing body in an amount suited for obtaining a required image density. The thus-applied liquid developer is fed to a latent area on an image-bearing body. In this case, since the liquid developer is circulated within the developing apparatus, and no volatile liquid is involved, a large-scale liquid collection apparatus is not required.
FIG. 11 is a view showing the configuration of a conventional toner recycling system (refer to Japanese Patent Application Laid-Open (kokai) No. 2001-305867) for recycling a developer (liquid toner) by the steps of collecting the developer remaining after use, measuring the concentration of the collected developer, and adjusting the concentration. A developer fountain collects not only the developer collected from a developing roller, but also carrier liquid, prewetting liquid, or the like collected from a photosensitive drum or an intermediate transfer body. On the basis of concentration measured by means of a concentration measuring unit, a concentration control unit causes the developer fountain to be replenished with carrier liquid and/or high-density developer so as to adjust the concentration of developer contained in the developer fountain to a predetermined level. Once adjusted to a predetermined concentration, the developer is fed in a usual manner to the photosensitive drum via an applicator and the developing roller.
The toner recycling system of the liquid developing apparatus can form, on the developing roller, a thin layer of liquid developer of an appropriate concentration and an appropriate amount. However, in view of the liquid developer being nonvolatile and highly viscous, desirably, a liquid developer having a more stable concentration is quickly formed and fed to the developing roller.
In the case of a conventional low-viscosity liquid developer, required solid content is relatively low. Thus, the low-viscosity liquid developer can be readily transferred by means of a pump. Also, the flow rate can be controlled by use of a flowmeter or the like installed in a transfer line. Further, concentration can be readily and efficiently controlled by, for example, the following method: the liquid developer passing through a slit is measured for light transmission density, and the measured transmission density is used to control the concentration. By contrast, a high-viscosity liquid developer involves difficulty in using a flowmeter, for the following reason. When the high-viscosity liquid developer is left stagnant for a long time in a pipe while in, for example, a nonpowered state, toner particles firmly adhere to the walls of the pipe and flowmeter. Further, particular technical devices must be adopted for concentration control.
In detecting the concentration of a high-concentration liquid developer by use of an optical sensor, a thick layer of the developer renders the optical sensor unusable. Specifically, in the case of a transmission-type sensor, the thick layer completely blocks off light. In the case of a reflection-type sensor, the thick layer causes saturation of reflected light. Thus, the thick layer prevents the optical sensor from detecting a high developer concentration that is required for development. In order to detect the concentration of the high-viscosity, high-concentration liquid developer, the liquid developer must be passed through a narrow gap so as to form a sufficiently thin liquid toner layer (a sufficiently thin developer layer) for measurement of concentration. Also, the high-viscosity developer adhering to a detection section must be mechanically removed. Similarly, when the concentration of the developer is to be determined from current that flows between electrodes, the developer must be passed through a narrow gap between the electrodes, and toner particles adhering to the electrodes must be continually wiped off.
An object of the present invention is to provide a toner recycling control system for a liquid developing apparatus that forms a thin developer layer on a developer-bearing body by use of a high-viscosity liquid developer, which system stably feeds the liquid developer of an appropriate concentration to the liquid developing apparatus, appropriately adjusts the concentration of the residual developer collected after development and after transfer, and feeds the adjusted developer to the developing apparatus.
Another object of the present invention is to quickly form a recycled developerxe2x80x94which is fed to the developing apparatusxe2x80x94from collected residual developer while accurately imparting a required concentration to the recycled developer.
A further object of the present invention is to stably measure the concentration of solid particles contained in collected developer (liquid toner) and enable checking for liquid toner deterioration.
The toner recycling control system of an electrophotographic apparatus of the present invention collects a post-development residual developer from a developer-bearing body of a developing unitxe2x80x94which performs development through formation of a thin layer of high-viscosity liquid developerxe2x80x94and a post-transfer residual developer from an image-bearing body; performs developer concentration adjustment to yield an adjusted developer; and feeds the adjusted developer back to the developer-bearing body. Thus, the toner recycling control system includes a concentration adjustment tank which stores a collected developer and is replenished with a concentrated developer and carrier liquid for developer concentration adjustment; and a buffer tank which receives and stores a liquid developer which has undergone concentration adjustment in the concentration adjustment tank. Once adjusted to an appropriate concentration, the liquid developer is fed to the developer-bearing body from the buffer tank.
A key to the toner recycling control system is to quickly and accurately attain a target developer concentration. To achieve the end, the present invention controls a collection pump, a feed pump, and a reflection-type concentration sensor. According to the present invention, a post-use liquid developer is collected to the concentration adjustment tank from the electrophotographic apparatus, which performs development by use of a high-viscosity liquid developer; and a high-concentration developer or carrier liquid is fed to the concentration adjustment tank in accordance with the detected concentration of the collected liquid developer to thereby adjust the developer to a predetermined concentration for recycling. The feed of a high-concentration developer or carrier liquid is controlled in the following manner: the amount of feed per unit time is varied according to the difference between a concentration sensor output and a target concentration.
The present invention includes an applicator roller for applying to a developing roller a liquid toner received from the buffer tank, so as to form a thin layer of liquid toner on the developing roller; a leveling blade for leveling the thin layer of liquid toner formed on the developing roller and for applying bias to the developing roller; an optical sensor for detecting the transmission density or reflection density of the thin layer of liquid toner after the thin layer of liquid toner is leveled by means of the leveling blade; and a detector for detecting current that flows through the leveling blade. The concentration and fatigue of the liquid toner are determined on the basis of a detection value of the optical sensor and current flowing through the leveling blade.